This invention pertains generally to a printer, and in particular to apparatus in a printer for adjusting the printhead-to-media spacing to accommodate different thicknesses of print media. Very specifically, the invention relates to mechanical apparatus which utilizes substantially normal carriage lateral motion for implementing desired changes in such spacing.
In a typical printer, such as an inkjet printer, the default printhead-to-media spacing is typically set to accommodate a commonly used, single-sheet-thickness, bond-weight paper, such as 20-lb. bond-weight paper. Envelopes and other print media are usually substantially thicker than a single sheet of such paper, and because of this, it is desirable to enable printhead-to-media spacing to be adjusted, either via user selection, or via automatic media thickness sensing, or both, so as to accommodate such thicker media.
To accomplish this kind of adjustment in the past, various approaches have been made which often involve the use of additional motors and electrical circuitry to effect changes in such spacing.
Typically, the carriage which supports the printheads is itself supported on two spaced structures, one of which is called a carriage rod, and the other of which is called an anti-rotation rail. The carriage is mounted for lateral shifting along and for rocking about the axis of the carriage rod. A portion of the carriage rides back and forth freely on the anti-rotation rail. Rocking of the carriage, which is usually produced by raising and lowering of the carriage where it overlies the anti-rotation rail, is effective to change printhead-to-media spacing. Additional motors and associated motor-driven mechanism, along with additional electrical circuitry, are what have often been introduced in the past to create such rocking of a carriage.
The present invention proposes apparatus for producing such an adjustment via actuators that engage mechanically when a printer carriage, which carries the printheads, shifts laterally under defined circumstances along the usual carriage support rod, and specifically beyond one, or the other, or both ends of the carriage""s usual lateral print-job range. Appropriate contact of these actuators causes an elongate finger to move into and out of engagement with an anti-rotation rail that is anchored to the frame of the printer. Such engagement causes a slight rocking motion to occur in the carriage about the axis of the carriage support rod, and this motion results in the desired, related change in printhead-to-media spacing. No additional motors or electrical circuitry are required.
Two embodiments of the invention are specifically disclosed herein. In each, an arrangement exists which accommodates two different printhead-to-media spacings. A greater number of spacings could, of course, be enabled if desired.
In one of these embodiments, a rotary shaft which moves back and forth with reciprocation of the carriage carries at its opposite ends a pair of helical cams. These cams, under certain circumstances explained below, engage stationary projections mounted on an otherwise conventional anti-rotation rail that fully supports the front part of the carriage. The carriage rests on the anti-rotation rail under the influence of gravity. The elevation of this front part of the carriage relative to the anti-rotation rail defines printhead-to-media spacing.
Cam and projection interengagement, under the influence of lateral carriage movement, and powered just by operation of the usual motor furnished for driving carriage reciprocation, produces, as required, the appropriate selectable change in printhead-to-media spacing. In particular, such cam/projection engagement causes a related angular rotation of the cam-carrying rotary shaft, which shaft also carries a rotatable bearing structure that includes a extending finger disposed to rotate with the shaft. This finger engages and disengages the anti-rotation rail, depending upon the angular disposition of the shaft. Engagement and disengagement of this finger with the anti-rotation rail is effective to lift and lower the front part of the carriage relative to that rail.
Printhead-to-media adjustment occurs in one direction (say, increasing) with the carriage moved laterally slightly beyond one end of its normal print-job travel range. It occurs in the other direction with the carriage moved laterally slightly beyond the opposite end of that range.
In the alternative embodiment of the invention described herein, printhead-to-media spacing adjustment occurs in an alternating-succession manner as a consequence of successive engagements between a single movable and a single stationary actuator, and with the carriage moved somewhat beyond just one end of its normal print-job range. The stationary actuator can be any appropriate structure, such as a portion of the frame in the printer. The movable actuator, which moves with the carriage, takes the form of a push-button which unidirectionally drives a spring-detented ratchet-like wheel which is drivingly engaged with a finger-like plunger. The plunger is driven successively either to occupy an extended position of engagement with the anti-rotation rail to lift the front part of a carriage, or to a retracted condition wherein it is effectively disengaged from that rail to allow the carriage to occupy a lowered condition relative to the rail. This adjustment mechanism accordingly acts in a somewhat bi-stable manner.